In the fabrication of electrical coils, and particularly such coils forming part of a transformer, it is not only generally necessary to provide insulation between adjoining windings and layers of windings of the coil, but also between the windings and the iron core associated with the transformer. U.S. Pat. No. 1,797,768 to Goad and U.S. Pat. No. 4,222,023 to Beech disclose arrangements for providing insulating wrappers about most or all of a coil, such as a motor winding. U.S. Pat. No. 3,657,677 to Hunt et al discloses an electrical transformer wherein a plurality of electrical coils are wound on separate coil forms. Each of the coils is attached to a separate insulating washer member, and the coils and washer members are disposed on a common insulating tube in side-by-side relation. The insulating washer members provide barrier insulation between coils.
U.S. Pat. Nos. 1,863,713 to Connor; 1,939,808 to Freeland and 2,511,174 to Osborne disclose coil arrangements in which an insulating member exists at one or both ends of a coil for insulating that coil end, as from a transversely-extending portion of the magnetic core. In U.S. Pat. No. 1,863,713 several fabric strips extend radially outward over the coil end face for providing such insulation. U.S. Pat. No. 1,939,808 discloses an arrangement in which a pair of insulative end caps are placed on the opposite ends of a coil and held in position by an insulative strip wound about the coil. U.S. Pat. No. 2,511,174 discloses a coil construction in which a bobbin core and end flanges are formed of insulative material such as cardboard. Several turns of the coil are wound about the bobbin core and the corners of the bobbin flange are then folded axially inward such that a subsequent layer of windings secure the bobbin flanges in position. These arrangements demonstrate varying degrees of complexity and cost associated with their manufacture.
In other recent arrangements, individual strips of adhesively backed insulation material have been manually positioned on each of the four perimeter regions at the end face of a coil, with eight such strips of insulation being required to insulate the two opposite ends of the coil. While such provision for insulating the ends of the coil may be relatively simple and effective, it is rather labor intensive and presents the opportunity for misalignment of the individual strips with the coil ends.